“0 .” — the domain refuses e-mail
Defined in RFC 7505 for domains that never receive mail. Senders fail immediately instead of retrying for days. Useful for parked and send-only domains.
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Free MX lookup
Find out which servers receive e-mail for a domain, in which order, and which provider runs them — Google Workspace, Microsoft 365, Zoho, Proofpoint and more. We also flag domains with no MX record or with a Null MX that refuses all mail.
Mail servers for
E-mail provider:
| Priority | Mail server | Role | Provider |
|---|
Next steps
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What is an MX record?
An MX (mail exchanger) record tells the rest of the internet which servers accept e-mail for a domain. When someone writes to [email protected], their mail server looks up the MX records of example.com and delivers the message to one of the hosts listed there.
Each MX record has two parts: a priority (a number) and a host name, for example “10 mx1.example.net”. The host name must have its own A or AAAA record: an MX cannot hold an IP address, and RFC 2181 and RFC 5321 forbid pointing it at a CNAME alias.
How MX priority works
Senders try the host with the lowest number first. If it does not answer, they move to the next one. Hosts with the same priority share the load, picked in random order.
The numbers themselves carry no meaning beyond their order — 1/5/10 and 10/20/30 behave the same. Backup MX servers with a higher number should apply the same anti-spam rules as the primary, or spammers will target them on purpose.
Special cases this tool detects
Implicit MX fallback
With no MX record, RFC 5321 tells senders to try the A/AAAA address of the domain itself. It is a legacy behaviour: publish real MX records — or a Null MX — instead of relying on it.
The domain does not exist
No record of any kind exists for the name. Addresses at such domains are undeliverable and should be removed from your lists.
Who handles the mail
MX host names reveal the provider: *.mail.protection.outlook.com is Microsoft 365, smtp.google.com and aspmx.l.google.com are Google, *.pphosted.com is Proofpoint, and so on.
MX records of common e-mail providers
What the MX records usually look like for the most common providers. Always copy the exact values from your provider’s admin console.
| Provider | Typical MX hosts |
|---|---|
| Google Workspace | smtp.google.com · aspmx.l.google.com, alt1–alt4.aspmx.l.google.com |
| Microsoft 365 | yourdomain-com.mail.protection.outlook.com |
| Zoho Mail | mx.zoho.com, mx2.zoho.com, mx3.zoho.com · mx.zoho.eu … |
| Proton Mail | mail.protonmail.ch, mailsec.protonmail.ch |
| Fastmail | in1-smtp.messagingengine.com, in2-smtp.messagingengine.com |
| iCloud Mail | mx01.mail.icloud.com, mx02.mail.icloud.com |
| Hostinger | mx1.hostinger.com, mx2.hostinger.com |
| Locaweb | mx.*.locaweb.com.br |
| KingHost | *.kinghost.net |
| GoDaddy | smtp.secureserver.net, mailstore1.secureserver.net |
| IONOS | mx00.ionos.com, mx01.ionos.com · mx00.kundenserver.de |
| OVHcloud | mx1.mail.ovh.net … |
| Cloudflare Email Routing | route1.mx.cloudflare.net, route2…, route3… |
| Proofpoint | mx0a-XXXXXXXX.pphosted.com |
| Mimecast | us-smtp-inbound-1.mimecast.com, eu-smtp-inbound-1.mimecast.com … |
| Barracuda | dXXXXXXa.ess.barracudanetworks.com |
| Amazon SES (inbound) | inbound-smtp.<region>.amazonaws.com |
Frequently asked questions
Is this MX lookup free?
Yes. You can run 100 lookups a day without an account (shared with the DNS lookup). The tool only reads public DNS records and sends no e-mail.
What does MX priority mean?
It is the order in which senders try the servers: the lowest number first. Equal numbers share the load. A higher number usually marks a backup server.
What happens if a domain has no MX record?
Senders fall back to the domain’s A or AAAA address (“implicit MX”, RFC 5321). If no mail server listens there, the message bounces. Domains that should not receive mail are better off publishing a Null MX.
What is a Null MX record?
A single MX record with priority 0 and host “.” (RFC 7505). It states that the domain accepts no e-mail at all, so senders give up immediately instead of retrying.
Can an MX record point to an IP address or a CNAME?
No. An MX must point to a host name that has its own A or AAAA record. Some servers tolerate a CNAME, but it breaks the standard and can cause intermittent delivery failures.
How do I know which e-mail provider a domain uses?
Look at the MX host names — this tool does it for you. For example, *.mail.protection.outlook.com means Microsoft 365, and aspmx.l.google.com or smtp.google.com mean Google. A security gateway such as Proofpoint or Mimecast can hide the mailbox provider behind it.
Does a valid MX record mean an e-mail address exists?
No. It only proves the domain can receive mail. Whether a specific mailbox exists is a different check — use the free e-mail validator for a single address, or validate a whole list with a free account.
How long do MX changes take to apply?
As long as the previous record’s TTL — often 1 hour, sometimes up to 24 hours or more. During the switch some messages may still reach the old servers, so keep them running for a day or two.
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